Racecar Engineering - September 2013

www.racecar-engineering.com September 2013

FORMULA STUDENT

T here is no doubt that hybrid and electric vehicles are taking centre-stage in

the modern automotive and motorsport industries. In 1997, it all started when the Toyota Prius became the first mass-produced hybrid vehicle; next was the first mass produced all-electric vehicle which came in the form of the Nissan LEAF in 2010. 2012 saw the first hybrid win at Le Mans by the Audi R18 e-tron Quattro and in March this year alone, more than 6.3 million hybrid vehicles were sold worldwide. This trend will undoubtedly continue, as 2014 becomes more electric than ever with the world’s first electric race at the launch of Formula E, and the increased usage of hybrid powertrains in Formula 1.

And it’s exactly the same for Formula Student.

The first electric Formula Student car to take part in a competition is thought to be what was called a ‘hybrid in progress’ (ie electric only), designed by the University of Florida for the 2007 Formula Hybrid competition. In the UK the bar was raised higher the same year with the introduction of a special alternative fuels category, dubbed class 1A. In 2012 it was decided to merge the classes

with both conventional and alternative powertrains running in the same class.

At the Silverstone competition this year, electric cars made up 20 per cent of the Formula Student field, which at first seems a relatively small proportion. However, overall first and second place were both won by electric teams. The main issue is the extravagant investment required for an all-electric concept, something which most universities cannot afford. Many teams, when asked, would go electric if they had

the extra funds, manpower and time required. The ‘electric percentage’ will undoubtedly increase over the coming years as more teams compete, the series becomes more global and students see the increased potential of electric powertrains.

Another record-breaking fact for this year’s competition: not only was it the hottest event held in the UK, but also the driest. Sun shades, shorts and regular barbecues made the paddock almost glamorous compared to previous years of trekking around in Wellington boots, battling with the wind and rain. Of course, with unexpected highs of 28degC (82degF), teams and their cars now faced an unknown challenge of dealing with the heat – most teams had

44

The 2013 Formula Student competition made worldwide motorsport history – an electric car beat a combustion car. And the surprises didn’t stop there…

Electric shock

BY GEMMA HATTON

ETH Zurich dominated the event with their all-electric car, the first win for an alternative fuelled vehicle in FSAE

Many teams said they would go electric if they had the funds, manpower and time required

Formula Student-SGAC.indd 44 29/07/2013 14:37

FORMULA STUDENT

September 2013 www.racecar-engineering.com 45

It is fairly unusual for the legality of cars to be protested at Formula Student

or indeed at any FSAE event, but that’s exactly what happened this year. During technical inspection the event officials suspected that the students of UAS Graz and Karlsruhe had not done all of the work on the engine themselves. Both teams use an AMG 595cc twin developed specifically for FSAE events. This led to the technical scrutineers requesting an official ruling as to the legality of the engines fitted to both cars, specifically in relation to section IC1.7 of the 2013 rules which states the following: ‘Turbochargers or superchargers are allowed if the competition team designs the application. Engines that have been designed for and originally come equipped with a turbocharger are not allowed to compete with the turbo installed.’

The concern was that from the start of the design process, the engine was designed with the turbocharger installed and this is the package fitted to both cars. It was not clear how much contribution was made by the students and how much by AMG.

The protest committee met and produced the following conclusions:

The intent of the regulations is that if an engine is purchased with a turbocharger fitted then it

should not be eligible for the competition with that turbo installation, so the team must design the installation of the turbocharger.

The fact that the engine was originally designed with this turbocharger should not be considered as an issue if the original design was produced by the students.

The main question to answer was therefore: did the team design the installation of the turbocharger?

After discussion between the protest committee and the team members and with feedback from other sources, it was concluded that the turbocharger installation had been designed by the team with appropriate levels of advice and support from AMG etc.

So the engines were deemed legal under the current regulations, but the information from the protest has been forwarded to the FSAE rules committee to consider future rules changes which could affect the legality of such engines and whether such engines conform to the spirit of the regulations. Many in the paddock have suggested that they feel future rules should only allow for commercially available mass-production blocks such as the Honda CBR or entirely student developed engines.

AMG’S CONTROVERSIAL ENGINE completed minimal testing, and those that did tested for a day at most in mixed conditions. It was going to be an interesting weekend, not least for those teams using electric drive. Some were even seen taping bags of ice to the electric motors ahead of dynamic events in an attempt to keep them cool.

The performance characteristics of the EVs were clear from the first dynamic events. Unsurprisingly, with torque instantly available, the electric cars dominated the acceleration event, claiming the top three positions, with the University of Stuttgart coming first, Delft University of Technology taking second and TU Dresden third, after the disqualification of the car from Karlsruhe (see p52).

The most visually obvious trend for this year’s cars was the integration of advanced aerodynamic packages, and there

were some highly interesting approaches, particularly for the acceleration event where reducing drag is essential. Most of the aero-dominant teams either adjusted parts of the rear wings, by altering the position of the slats to reduce frontal area, and therefore drag, or dropped the entire rear wing assembly down to increase top speed. This may seem an obvious tactic, but to actually implement adjustable aero into a Formula Student car can be extremely challenging and demonstrates a high level of forward thinking from the teams. It is fair to say that this year’s aero designs were the most extravagant, with the Karlsruhe Institution of Technology team running a full DRS system, which gained their combustion car sixth place in acceleration. However, the most striking aero design by far was the Warsaw team from Poland which ran two rear wings, a front wing and an underfloor.

The same form was repeated in the sprint with the top three

all being electric. TU Delft coming first this time with a fastest time of 51.365, the Stuttgart car was close behind at 51.795, and only a tenth of a second denied Zurich second place. They finished third.

The toughest event is left until last and is the Formula Student equivalent of a grand prix. With 22km to complete, including a mandatory stop, driver change and hot restart the car’s reliability is pushed to its limits, and with 300 points up for grabs, completing the endurance discipline is what every team works towards. Every year cars fail, don’t restart or even catch fire which completely changes the standings. This year, however, with the added factor of the extreme heat, only 21 teams finished. That means 68 per cent of the cars failed – the highest dropout rate recorded.

In the past, the notorious Silverstone weather has caused

havoc with sudden heavy rain, so for this year’s event, the top 10 cars from the sprint event took to the track at the same time in a ‘shoot-out’ to make it fairer, and – unsurprisingly – there was plenty of drama. The first teams on track were Zwickau, Karlstad and the University of Bath who were the fastest car, lapping at 65.1 seconds. After overtaking Zwickau, Bath then found themselves stuck behind TU Graz, who were a few laps in and ignored three blue flags. Last year’s winning Chalmers started their endurance, but only survived three laps before a rear left wishbone failure – a real shock for such a popular front-runner. Next to join was the Munich team, with their monster rear wing, but their car only lasted two laps due to a driveshaft problem. Zurich began their race, while the Bath car was next to fail at the driver changeover when the engine failed to restart. Karlstad followed suit by also retiring

The Warsaw team ran a striking design featuring two rear wings, a front wing and an underfloor


FORMULA STUDENT


TU Delft’s electric car was a much fancied runner, but failed to deliver

I am frustrated by a few things from this year’s FSAE competitions, but one gripe

has been with me for some years now and I’m fed up of it! It concerns carbon fibre chassis. For me these are all of very bad design indeed, not as engineering objects themselves – indeed some of them are very nice – but as objects designed to fulfil a specific purpose. In the rules there is a very clear statement, indeed it’s rule A1.2, almost the first rule in the book: ‘For the purpose of the Formula SAE competition, teams are to assume that they work for a design firm that is designing, fabricating, testing and demonstrating a prototype vehicle for the non-professional, weekend, competition market …additional design factors to be considered include: aesthetics, cost, ergonomics, maintainability, manufacturability, and reliability.’

I have been increasingly of the opinion that this rule is being largely ignored. I have been that amateur weekend racer mentioned in the rules, and I know many others. To a man they all say that they would not buy a car with a composite chassis. ‘Too expensive,’ they say, ‘if you crash it – which if you drive like we do you will, a lot – you can’t tell how bad the damage is without specialist equipment. And if you have a really good hit, you’ll probably write the chassis off as they are near impossible to repair.’

Further to this, amateur racers look for longevity from their chassis. Formula Ford 1600 chassis racing today are

often more than two decades old – indeed I used to race a 1960s Formula Vee chassis against 21st-century designs, and it could corner with the best of them. The life of a composite chassis is not fully understood, but the consensus in the sport seems to be that they are only good for three or four years before needing either replacement or major repair work. Something else that makes them really unrealistic for the non-professional, weekend, competition market. Students argue that carbon fibre chassis must be the best route because ‘that’s what they do in F1’. They contest that the composite tubs are lighter and stiffer. This is certainly true, but they have lost sight of the point of the competition. F1 teams do not build cars for the non-professional, weekend, competition market despite the performances of some pay drivers at the back of the grid.

What frustrates me is that the design judges in all competitions seem to have forgotten this too, or simply don’t realise that composite cars don’t comply with rule A1.2, and we regularly see carbon chassis cars in the design finals. Yes the carbon cars with big budgets are very nice things with good aesthetics and ergonomics, but to my mind I cannot see how they can get good points in the design competition as they fall down on the cost, maintainability, manufacturability, and reliability criteria. But then I suppose I’m not a design judge.

Sam Collins

from the race, as the all-famous Delft team came off the start line, but without their new aero package. The electric Karlsruhe car joined the track but due to previously breaking the rules, (see sidebar, p52), their car was running at a very slow 1 min 16 secs per lap. Zwickau were the first of the top 10 to finally complete the event.

Meanwhile another previous winner, Delft, aborted their race after a disappointing four laps. The electric Stuttgart car joined the drama, but theirs was a short-lived race due to steering issues on the first lap. Another one bit the dust as TU Graz pulled to the side of the track with smoke and steam billowing out of their car, causing a major hold-up for the rest of the teams. The second car to cross the line was Zurich, which only left Karlsruhe running, but that car had damage to one of its motor-gear units. So, out of the top 10 of the best Formula Student teams in the world, only two finished, which although disappointing, made for a very interesting results table.

Outside of the top 10 shoot-out, the endurance event continued to be just as dramatic. The battle of the Brits continued

as Hertfordshire completed 15 laps before an electronics failure struck, while Oxford Brookes also dropped out with a broken exhaust, which burnt the car’s chassis badly. That left the competition wide open for the overall best Brit position.

Stuttgart’s combustion car was one of the few to finish, and

came a close third behind Zurich, which won ahead of Zwickau.

After an eventful five days in Silverstone, the overall winner was a fight between the two electric machines of Zurich and Zwickau. But with Zwickau just behind on five out of the eight judged events, Zurich won by 70 points, with the successful endurance result helping Stuttgart Combustion to take third.

The top British team only finished 15th, but that was a fantastic achievement for the University of Huddersfield – which proves the effectiveness of having a reliable car that scores consistently. The other surprises were last year’s winners, Chalmers, finishing 17th and the event favourites, Munich and Karlsruhe electric coming 27th and 30th respectively.

Out of the top 10 best Formula Student teams in the

world, only two finished

COMPOSITE CONTRAVENTIONS

The UAS Dortmund chassis, one of many composite-built models on show


RT Quaife Engineering Ltd

Vestry Road, Otford, Sevenoaks

Kent, TN14 5EL

United Kingdom

QUAIFE FP SEPT13.indd 1 23/07/2013 13:16


FORMULA STUDENT

48

OVERALL WINNER: ETH ZURICH

Once the Karlsruhe electric car had been disqualified from two dynamic

events, it is fair to say that the competition was essentially dominated by the team from Switzerland. Its neat electric car impressed many including the design judges, winning that event. The major development for the electric teams this year was the integration of four wheel drive, which Sven Rohner, ETH Zurich’s team leader explains. ‘This year we focused on our drivetrain concept. We changed it from last year’s rear wheel drive to a four wheel drive system, which is a major challenge because not only do we have more motors, but more electrical components and therefore more noise within the communication lines.’ Last year, Zurich ran two outer run AC hub motors, whereas this year’s car features four internal

AMZ M3 AC hub motors which were entirely made by the team. Weighing in at 5kg, the new designs produce the same power as the previous model (32kW) but are 40 per cent lighter. ‘The motors are something we are really proud of because we started with a white piece of paper and developed the

electrical and the mechanical aspects, which allowed us to alter the moment curves and generate efficient designs.’

Composite chassis remain controversial in FSAE, and many consider them to be outside of the spirit of the competition, but the Swiss team has been running carbon fibre

monocoques since 2008, and Rohner believes that is the right choice, ‘F1 use carbon fibre monocoques and it is possible to repair because if you know from the beginning then you make decisions when designing other parts to accommodate repair. Also, as it is naturally stiffer than a normal steel spaceframe, monocoques are the way to go for increased performance.’ Due to implementing the hub motors, the surface area of the chassis could be reduced, allowing the chassis weight to be reduced by 13.3kg.

Another weight saving measure is the use of composites in the wheel rims. While far from unique in FSAE, the Swiss designs are very neat indeed. ‘They are single piece and weigh around 850g – one of the lightest in Formula Student. If compared to common aluminium shells, our rims are

This year’s ETH Zurich car featured four internal AMZ M3 AC hub motors produced from scratch by the team. They produced the same power as their predecessor, but came in at 40 per cent lighter

"The composite wheel rims are single piece, weighing around 850g"


ENGINEERING THE ADVANTAGETHROUGH QUALITY DESIGN

Our innovative design and precision performance engineering makes usyour perfect Motorsport partner. Our world-class engineers arecommitted to delivering world class services where your exactingrequirements will be mirrored by our exacting standards.

Contact us to see how we can engineer your competitive advantage.

T. +44 (0) 1480 [email protected]

www.titan.uk.net Dynamic Engineering

��

49_RC_0913.indd 28 30/07/2013 09:47


FORMULA STUDENT

50

less than half the weight, yet double the stiffness and have increased yield strength.’ Of course, with the integrated gear and hub motor on a 10-inch wheel, space is somewhat restricted. ‘It is really on the edge and tight in there, which is another advantage of our self-developed rims,’ says Rohner, ‘because we can design it to be stiffer, to allow us to go a little tighter – something we wouldn’t have been able to do with aluminium shells.’

Like most of the top cars in the 2013 competition, the ETH Zurich car features large wings, and the trend towards downforce-generating devices has come as no surprise to the Swiss students – it was the first team to fit wings to an electric FSAE car. ‘Last year, aero was more of a “nice to have” feature,’ Rohner adds. ‘Although we completed simulations, wind tunnel and track testing, it wasn’t a fully integrated package – so we could run without it if there were any problems. After learning the performance gains from last year, we integrated

aerodynamics into every single part right from the beginning.’ A front and rear wing, shaped undertray and rear diffuser made up the aero package. Particular attention was paid to the font wing as this controls the entire aerodynamic characteristics of the car. According to the team, the overall aero package increased the downforce by 30 per cent while maintaining the same level of drag.

While the high temperature endurance caused many top teams issues, the Zurich car ran strongly and quickly. ‘One of the reasons why we finished endurance was because we really pushed the manufacturing of our car to be complete by May,’ Rohner says. ‘We had a lot of time to evaluate and deal with all the issues, but you also need luck, and we were lucky to be able to fix all the problems we had to finish the race.’

It is likely that some teams in the future will copy, or at least be heavily influenced by, the Zurich design, but Rohner believes it is inevitable anyway as he feels that the design concepts of top teams are converging. ‘In the last three to four years, we have seen major concept changes for electric cars. For instance, our team started with DC motors, no aero and 13-inch rims. Now with 10-inch rims, four wheel drive and an integrated aerodynamic package. This is the winning concept, which is proved by other top teams such as Delft and Karlsruhe.’ If that is the case then expect to see a range of similar cars in 2014.’

OVERALL WINNER: ETH ZURICH (continued)

Length: 2930mm

Width: 1410mm

Height: 1550mm

Wheelbase: 1240mm

Track: 1200/1160mm

Weight – no driver: -170kg

Weight – distribution including driver: 107kg/131kg

Suspension: Double unequal length A-arm. Pushrod actuated horizontally oriented air springs and oil dampers

Tyres: 18.0x6.0-10 Hoosier LC0/R25B

Wheels: 6.5-inch single-piece CFRP

Brakes: Floated, hub mounted, 190mm dia., water-jet cut

Chassis construction: Single-piece CFRP monocoque

Engine: 4xAMZ M3 electric motor

Fuel system: Lithium polymer accumulators

Max power: 4x35kW @ 16.000rpm

Max torque: 4x28Nm @ 0rpm

Transmission: 1.5 stage planetary gearbox

Differential: None

Final Drive: 1:11.8

TECH SPEC

"This is the winning concept, which is proved by other top teams"


The best connection systems made.www.bmrs.net

UK: Unit 5 Chancerygate Bus Ctr. / St.Mary’s Rd. / Langley, Slough SL3 7FL / 01753.545554US: 4005 Dearborn Place / Concord, NC 28027 / 704.793.4319 BM

RS-U

K-20

12

Cams + Pulleys, Belts & Chains Valves & Valve Springs Performance Cam Kits & Valve Spring Kits Followers & Tappets

Kent Cams – the best in Europe: No.1 for product development expertise The greatest performance increase of

any single modification The widest range of camshaft

ancillaries produced on site

The most advanced technology: Negative radius to -35mm CBN wheels with constant surface speed Multi-angle lobes with CNC dressing Marposs 3D C and Z axis position probe Microphonic wheel dressing Lotus Concept Valve Train software

-35mm Worlds apartOur technology centre is the most advanced in Europe.

That is how we can achieve a negative radius of up to -35mm. Extreme engineering and precision that other performance cam manufacturers in Europe cannot match. All our camshafts and ancillaries have been developed by the best to be the best.

KCTech135x188-aw4.indd 1 20/12/2011 11:39

51_RC_0913.indd 28 30/07/2013 09:48


FORMULA STUDENT

52

Had it not been for its double disqualification from dynamic events, the

electric car from the Karlsruhe Institute of Technology would have challenged for the overall win. It certainly was a neat piece of design, complete with a fully functional DRS wing. Its aerodynamic package was an area that even the team were not entirely convinced about, as team captain Benedict Jux explains. ‘This car is our second with an aerodynamic package, and it’s hard to define how effective it is,’ he says. ‘It has some positive aspects, especially for an electric car. It’s difficult to design because of the drag and the efficiency. It improves performance during skidpad and autocross and especially during the endurance, but if you have some problems or need some more energy it can be a burden. That’s why this year we designed DRS to decrease drag and improve the efficiency.’ Most of the evaluation work was done using CFD, and the team were keen to point out that they used Star CCM software to develop it, but they also had not ignored some well-proven techniques, and wool tufts were evident on the underside of the wing when the car arrived at Silverstone.

Aerodynamics aside however, most of the work on the car was put into its four wheel drive powertrain. Unlike other cars driving all four corners, the Karlsruhe car does not use hub

motors – instead it is fitted with four inboard IPM motors.

‘The special thing is the drivetrain,’ says Jux. ‘It’s the first Formula Student car with this type of drivetrain, no one tried this concept before. The four-wheel drive concept that we built in the last few years was a centre motor in the back and the wheel hub motors in the front. This year two teams are having just wheel hub motors, which have much more unsprung mass. We decided that for the performance of the car, it is better to put the motors in the centre to reduce unsprung mass and lower the centre of gravity. The challenge is probably the dynamic control, if you want to use the advantages of the four wheel drive, but to get it to work it’s not that difficult. All four wheels turn forward.’

Reducing unsprung weight was a key aim for the Karlsruhe team, and for that reason it

moved to smaller 10-inch wheel rims. ‘I think you can see on our car that one main goal was to reduce the unsprung masses. We did some tests at the beginning and bonded some weights into the uprights which had a big influence – up to three-tenths difference per lap just because of the increase unsprung mass. So for the wheels we have gone smaller, it has lower masses and less rotational inertias. Most teams have changed and the results from the event show that better teams prefer 10 inches.’ But the smaller rims create their own issues especially when they are made from carbon fibre which has a direct influence on brake temperatures.

‘We don’t have any experience about 10-inch rims and our brakes,’ says Jux. ‘Our brake manager says that he’s not really sure this will work out for the whole of endurance so we

have fitted brake ducts just for safety reasons. It’s not a problem we have had with 13, but we heard of some problems from other teams last year, especially with CFRP rims. The rims are really hard to develop.

‘We had a 13-inch rim which took about two years to develop, but now we have this which we will carry over on to future cars. They give weight reduction and maybe a little bit of stiffness, but if you know how stiff your rim is, you can manage it with other parts.’

Just how strong the Karlsruhe car really was will probably never become clear. It was certainly fast, but it was not legal, and when running in fully legal specification in the endurance it lacked pace. But the team were worried if it would go the distance on a single charge anyway.

A number of teams were disqualified from the acceleration event at Silverstone, all of whom were running electric cars. Karlsruhe, University of Southern Denmark and Group T International University College were all found to have breached part EV2.2 of the 2013 Formula SAE technical regulations which states that: ‘The maximum power drawn from the battery must not exceed 85kW. This will be checked by evaluating the Energy Meter data. A violation is defined as using more than 85kW for more than 100ms continuously or using more than 85kW, after a moving average over 500ms is applied.’ The penalty for this is disqualification and all three were removed from the results. The biggest loser was Karlsruhe, which had won the event before its disqualification. It then repeated the violation in the sprint event and lost another strong finish, taking it out of overall contention. PENALTY: DISQUALIFICATION

CAUGHT

KARLSRUHE

A lot of development was put into the four wheel drive powertrain


AT THE HEART OF THE WORLD’S

MOST POWERFUL ENGINES

Give us your requirements and we’ll find a high-performance solution,no matter how extreme.

Call our sales team: +44 (0) 1455 234200 Email us: [email protected]

www.arrowprecision.com

Untitled-39 1 16/07/2013 13:38


FORMULA STUDENT

54

It often seems that Formula Student is driven by the need for weight reduction. Over

the last few years, teams have been downsizing their engines from four to two cylinders to reduce weight. More and more teams have been trading their steel spaceframe chassis for full carbon fibre monocoques to reduce weight. This year was no different, as teams switched from 13-inch to 10-inch wheels; to reduce weight. Indeed the overall top four cars had 10-inch wheels.

The theory behind the smaller wheel is not only the weight saving, but the effectiveness of the weight saving in that area. As you may know, unsprung mass is defined as the total weight of components that are not supported by the suspension, which includes the wheels, tyres and uprights. The importance of reducing this mass is because it is effectively uncontrolled, so the lighter it is, the better the contact between the tyre and the road surface.

After evaluating the dynamic equations, the translational and rotational inertia effects of a wheel can be expressed as an equivalent non-rotating mass, therefore it can be proved that the equivalent mass of a tyre is twice its static mass. In numbers this means that if 0.5kg is shaved off each wheel, it would feel 1kg lighter. Multiply this by four and you can quickly see the huge gains in weight reduction that can be made. The knock-on effect of reducing the rotating inertia is that it improves the performance drastically, as more power is available to accelerate the car, provided you are not traction limited, in which case the performance gains will still be made, just at higher speeds. Another benefit, although relatively small in comparison, is the effects under braking, as less rotating inertia reduces the brake load, and therefore heat.

‘The main advantage of the 10-inch is the weight saving and the improved acceleration characteristic due to the smaller

circumference of the wheel, and therefore the lower final drive,’ says Oliver Hickman, consultant manager from Brunel Racing. ‘Whether or not we downsize for next year is a tough call because it would change how we run the engine – we’re currently setup to compensate for the 13-inch wheels, so we still get the good acceleration. The risk you get on the 10-inches, especially in damp conditions, is the increase in wheelspin due to the higher acceleration, as most teams don’t have intermediate tyres. With the 13-inch you have a higher top speed. Although it’s not a massive difference, it’s definitely something we need to test and verify.’

The smaller wheels require smaller components, so downsizing not only has the

multiple benefits of reducing inertia, but also the knock-on effects of even more weight reduction. However, the 10-inches do create major disadvantages – yet the constant push for lightweight concepts make these a small sacrifice, as the Stuttgart combustion team described: ‘Of course the packaging is very difficult with the brakes, because the system is very small and therefore gets hot easily and quickly. Also, as the front wing blocks air getting to the brakes, we’ve added brake ducts for cooling to utilise the flow from under the wing to travel into the duct. There are some disadvantages, but in the end you get more points with the 10-inch wheels than without.’

Marcus Linder, team leader for Chalmers, agrees. ‘It’s basically

due to the weight saving. Although the data does show the 10-inch wheels are worse in terms of peak lateral force and tyre temperatures, the gain we see in having less unsprung mass is worth the change.’ A further trend is the teams that run the 10-inches now make them wider. ‘We can get a better response and behaviour from the tyre when it is wider due to the increased contact patch,’ says Chalmers, ‘and the widening doesn’t affect the maximum lateral force too much.’

Not only has the actual size of the wheel changed for weight reduction, but the design of the wheel too, with some teams now developing carbon fibre rims.

David Turton, driver for Team Bath and next year’s project manager describes their concept: ‘This year was the first time we’ve run carbon fibre rims with an aluminium centre and we have saved an approximate 600g per wheel. As well as this, there are stiffness gains to be made as the camber control is improved. Naturally, the design on CAD differs to real-life when the car is fully loaded, as it all deflects, which is why stiffness is so vital, because it directly relates to wheel control. We tried developing the rims in 2011, but it’s only this year that they were fully ready to implement on the car, which has just come from refining the design and practising the in-house lay-up technique. The lightest carbon wheels on the grid are on TU Graz and Zurich, which have a three spoke carbon design and weigh in at just under 900g per wheel.’ As impressive as this sounds, whether these lightweight wheels actually run in the race is another question. However, carbon rims look like the future, but once again the development costs and time required are powerful factors in determining just how many teams we will see with them next year.

WHEELY SMALL

"Downsizing for next year would change how we run the engine"

10-inch wheels offer a substantial weight saving, but there are disadvantages


Take cutting-edge wind tunnel technology. Add a 180 mph rolling road.

And build in the best in precision data acquisition capabilities. When we

created the world’s first and finest commercially available full-scale testing

environment of its kind, we did much more than create a new wind tunnel.

We created a new standard in aerodynamics.

1 8 0 M P H W I T H O U T M O V I N G A N I N C H

+1 704 788 9463 INFO@WINDSHEAR INC .COM W INDSHEAR INC .COM


FORMULA STUDENT

56

T he use of aerodynamic devices is quickly becoming a necessity in

Formula Student. Last year, after the monster rear wing fitted to the Monash car, more wings, diffusers, undertrays and active aero concepts were seen at Silverstone than ever before.

‘It’s amazing the difference it makes, despite the fact that we race at very low speed,’ explains Dave Turton, current driver and next year’s project manager for Bath University. ‘The average

corner speed is 40-50km/h, so you would think that it’s not fast enough for aero benefits. We have done back-to-back comparison with and without the wings and have found lap time. However, this is mainly due to driver confidence when braking.’

Bath have quite a small aero package when compared to other teams such as Munich and Monash, which is nearly three times the chord length, yet still weighs a small 10kg.

‘It then becomes a trade-off between downforce and mass,’ adds Turton. ‘If you have advanced manufacturing processes that make the wing lighter, you can run larger wings, yet still achieve the same centre of gravity and mass penalty. Our aero is approximately 11-12kg including the mounts.’

Monash are renowned as the ‘pioneers’ of aero in the Formula Student world and it has been their area of focus since the very beginning. Of course, access to their own full-scale wind tunnel has helped. Monash state that their size wings are the absolute minimum required to actually gain a benefit, in which case the circuits may need to become a little wider.

AERO RESISTANCEOne team that has resisted the challenges of aero until this year was Delft, which believes that bigger is not always better. ‘It’s been really difficult, but luckily we have a lot of aerospace engineers in our team,’ said a representative. ‘We also have great facilities at our university so we complete wind tunnel testing on scale and full-size models, and so far the rear wing produces roughly the same amount of downforce as the CFD predicts. With the massive wings you see on other cars, you just add weight, which doesn’t make sense for our lightweight concept. This year with the simulations we concluded that an aero package would give us more points in the competition, but maybe next year the rules change and aero may not be so important.’

As mentioned in the race report, the adjustable aero systems were also making appearances this year with both the electric and combustion cars from the German Karlsruhe team running a very F1-style DRS. However, many of the teams, such as Chalmers, don’t see the benefit, as team leader Marcus Linder suggests. ‘We did the analysis into whether

it would be worth having DRS,’ he said. ‘But even though there is a potentially small gain, it introduces many problems from the control side as it adds complexity. However, we do adjust the wing depending on the type of event, but once it’s running the aero remains static.’

Other teams have similar approaches, such as Team Bath. ‘For the acceleration event we tried to neutralise the rear wing by adjusting the trailing edge. It costs nothing to implement other than a few extra holes in your sideplate, provided you’re not traction limited at high speed. In terms of DRS, it is a difficult one. In Formula Student you have no chance to learn the circuits, so to not only learn them and learn the use of DRS could be driver overload. It’s also extremely risky because if the DRS stays open you’ll lose a lot more time in that scenario, than the gain you would make with it fully working.’

A valid point, as Mercedes ably demonstrated with Michael Schumacher’s DRS a few seasons back. However, this is not stopping teams from developing active aero, as Turton commented: ‘A team in Oklahoma has an active front and rear wing, which is impressive, so all their multiple elements in the wing open and close when the car drives into corners. Another American team has an active rear wing that splits, so that they can activate half of the rear wing depending on the steering angle. Therefore, when they turn into a corner they use the angle of attack on one side of the wing to counteract body roll and increase the vertical force on the inside tyres. Of course, in theory it is interesting, but in practise if you’re counter steering, the system could be unstable unless you have an advanced control system. Nonetheless, the corners at Silverstone are relatively slow speed, so just how much benefit do you really get from aero?’

ADJUSTING AERO

"It’s amazing the difference it makes, despite the low speeds”

Karlsruhe’s car was also bewinged. Note the wool tufts on the underside

The Polish entry had the biggest wings, but perhaps not the most effective


Racecar Engineering - September 2013

Documents

Transcript of Racecar Engineering - September 2013